What is the role of ketamine (anesthesia medication) as an adjuvant in spinal anesthesia?

Ketamine as an Adjuvant in Spinal Anesthesia

Primary Recommendation

Ketamine may be used cautiously as an adjuvant during spinal anesthesia, but its routine use is not recommended due to limited evidence of benefit and significant risk of postoperative confusion, particularly in elderly patients. 1

Evidence-Based Considerations

Potential Benefits

The theoretical advantages of ketamine in spinal anesthesia include:

• Counteracting hypotension through sympathomimetic activity, which may help maintain blood pressure during neuraxial blockade 1
• Bronchodilation effects that could benefit patients with asthma or chronic obstructive pulmonary disease 1
• Supplemental analgesia without respiratory depression when used in subanesthetic doses 1

Significant Risks and Limitations

The most concerning adverse effect is postoperative confusion, which is particularly problematic in elderly patients undergoing spinal anesthesia. 1 This population already has limited physiological reserve and increased vulnerability to cognitive disturbances.

Additional risks include:

• Emergence phenomena occur in approximately 12% of patients, including hallucinations, delirium, and irrational behavior 2
• Increased secretions when combined with other medications, potentially causing upper airway complications 1
• Behavioral changes including blunted affect, catatonic state, and nystagmus 3
• No proven benefit for delirium prevention: The PODCAST trial (672 patients) found no difference in postoperative delirium rates between ketamine and placebo groups (19.45% vs 19.82%, p=0.92), with increased hallucinations (20-28% vs 18%) and nightmares (12-15% vs 8%) in ketamine groups 1

Clinical Context Matters

For hip fracture surgery in elderly patients specifically, ketamine should be used with extreme caution if at all. 1 The guideline explicitly states that while ketamine may theoretically counteract hypotension, it may be associated with postoperative confusion in this vulnerable population.

For opioid-tolerant patients undergoing spine surgery, ketamine shows more promise. 4 A prospective randomized trial demonstrated that subanesthetic ketamine (0.2 mg/kg bolus followed by 2 mcg/kg/hour infusion) significantly reduced pain scores in narcotic-tolerant patients during the first postoperative day (NRS 3.6 vs 5.5 at rest, 5.6 vs 8.0 with physical therapy).

However, in opioid-naïve patients undergoing lumbar fusion, ketamine provided no sustained benefit. 5 Pain scores were lower only at 4 hours postoperatively, with no difference in opioid consumption at 48 hours.

Practical Algorithm for Decision-Making

When to Consider Ketamine:

1. Patient is opioid-tolerant AND undergoing major spine surgery 4
2. Severe refractory hypotension during spinal anesthesia despite standard management 1
3. Patient has significant bronchospasm requiring bronchodilation 1

When to Avoid Ketamine:

1. Elderly patients (>65 years) - highest risk of emergence phenomena and confusion 1, 2
2. Outpatient procedures - unless patient can be accompanied by responsible adult and monitored until complete recovery 2
3. Patients with psychiatric history - increased risk of adverse psychological reactions 2
4. Routine use for delirium prevention - no evidence of benefit 1

Dosing Recommendations (If Used)

If ketamine is deemed necessary, use the lowest effective dose to minimize adverse effects: 1, 2

• Intravenous bolus: 0.2-0.5 mg/kg 4, 3
• Continuous infusion: 2 mcg/kg/hour (0.002 mg/kg/hour) for postoperative analgesia 4
• For sedation during spinal: Use with extreme caution; midazolam or propofol are preferred alternatives 1

The 100 mg/mL concentration must be diluted before intravenous administration. 2 Administer slowly over 60 seconds to avoid respiratory depression and enhanced pressor response.

Mitigation of Adverse Effects

To reduce emergence phenomena: 2

• Minimize verbal, tactile, and visual stimulation during recovery (while maintaining vital sign monitoring) 2
• Consider co-administration with benzodiazepines (though this may prolong sedation) 1, 2
• Use lower doses in conjunction with other analgesics 2
• Have short-acting barbiturates available to terminate severe emergence reactions 2

Superior Alternatives

For most patients undergoing spinal anesthesia, better adjuvant options include: 1

• Intrathecal fentanyl (preferred over morphine/diamorphine due to less respiratory and cognitive depression) 1
• Peripheral nerve blockade (femoral nerve or fascia iliaca blocks) for extended postoperative analgesia 1
• Low-dose intrathecal bupivacaine (<10 mg) with positioning strategies to reduce hypotension 1

Regional analgesia demonstrates clear benefit: A randomized trial in hip fracture patients showed fascia iliaca blocks reduced delirium incidence (10.78% vs 23.8%, RR 0.45), severity, and duration compared to sham blocks. 1

Bottom Line

Ketamine's role as an adjuvant in spinal anesthesia is limited and should be reserved for specific clinical scenarios (opioid-tolerant patients, refractory hypotension, severe bronchospasm) rather than routine use. 1 The risk-benefit ratio is particularly unfavorable in elderly patients, where postoperative confusion can significantly impact outcomes. 1 Peripheral nerve blockade and intrathecal opioids provide superior analgesia with better safety profiles for most patients undergoing spinal anesthesia. 1